Conventionally, as air-conditioning devices for transferring heat between indoors and outdoors, there have been air-conditioning devices comprising a usage-side heat exchanger disposed indoors and a heat-source-side heat exchanger disposed outdoors. In an air-conditioning device of such description, in order to transfer heat, one of the usage-side heat exchanger and the heat-source-side heat exchanger is used as a radiator, and the other is used as an evaporator. For example, in air-conditioning devices of such description, a refrigerant is circulated between the usage-side heat exchanger and the heat-source-side heat exchanger and heat is transferred; therefore, a refrigeration device is generally configured using a compressor for compressing the refrigerant, and the usage-side heat exchanger and the heat-source-side heat exchanger (radiator and evaporator).
In a refrigeration device of this type, if the lubricating oil temperature (hereafter referred to as “oil temperature”) is low when the pressure in the crank case is under a fixed condition when the compressor is stopped, the proportion of the refrigerant dissolving into the lubricating oil in the crank case increases. Under additional conditions such as a long-term shutdown of the compressor and/or a change in the temperature of the refrigerant or temperature of external air, the phenomenon that we call “refrigerant stagnation” occurs, and a large amount of the refrigerant solves into the lubricating oil in the compressor under the refrigerant stagnation. When the refrigerant stagnates into the lubricating oil, e.g., the viscosity of the lubricating oil decreases and the performance of the lubricating oil decreases.
Accordingly, in order to prevent refrigerant stagnation in the compressor, measures have conventionally been taken to mount a heater to the crank case and warm the compressor and prevent the refrigerant from stagnating even when the compressor is stopped. There are also instances in which the lubricating oil in the compressor is warmed by motor coil heating using open-phase energization.
However, energizing the heater to warm the compressor presents a problem in that a given amount of power (standby power) is consumed, increasing the amount of power consumed by the refrigeration device.